A combustion apparatus having: an upstream-side air supply chamber and a downstream-side mixing passage, both being respectively interposed between a fan and a burner; and a zero governor which is interposed in a gas supply passage and which adjusts a secondary gas pressure to a pressure equivalent to an internal pressure in the air supply chamber, thereby enabling to maximize a turndown ratio to the extent possible. The combustion apparatus has: first and second, totally two, mixing passages; a first gas outlet which is in communication with a narrowed part of the first mixing passage; a second gas outlet which is in communication with a narrowed part of the second mixing passage; a first air valve which varies an opening degree of an air inlet of the first mixing passage; a second air valve which varies an opening degree of an air inlet of the second mixing passage; and a gas valve.

A combustion apparatus having: an upstream-side air supply chamber and a downstream-side mixing passage, both being respectively interposed between a fan and a burner; and a zero governor which is interposed in a gas supply passage and which adjusts a secondary gas pressure to a pressure equivalent to an internal pressure in the air supply chamber, thereby enabling to maximize a turndown ratio to the extent possible. The combustion apparatus has: first and second, totally two, mixing passages; a first gas outlet which is in communication with a narrowed part of the first mixing passage; a second gas outlet which is in communication with a narrowed part of the second mixing passage; a first air valve which varies an opening degree of an air inlet of the first mixing passage; a second air valve which varies an opening degree of an air inlet of the second mixing passage; and a gas valve.

In a stack leading from a fired heater, a plurality of damper blades are positioned at a longitudinal location, each blade being at least partly rotatable around its longitudinal axis to regulate flow through the stack. A plurality of controllers is operatively associated with the plurality of parallel blades to effect rotation of the blades. At least one of the controllers is decoupled from the rest of the plurality of controllers and used to independently control at least one but not all of the plurality of damper blades. The damper blades can be parallel or opposed.

In a stack leading from a fired heater, a plurality of damper blades are positioned at a longitudinal location, each blade being at least partly rotatable around its longitudinal axis to regulate flow through the stack. A plurality of controllers is operatively associated with the plurality of parallel blades to effect rotation of the blades. At least one of the controllers is decoupled from the rest of the plurality of controllers and used to independently control at least one but not all of the plurality of damper blades. The damper blades can be parallel or opposed.

A damper control device may include an appliance control programmed processor for controlling a gas burner, the appliance control programmed processor including a lockout register for storing electronic data information, and a damper control programmed processor for controlling a damper, the damper control programmed processor including a damper request register for storing electronic data information. The damper control programmed processor may be configured for selectively opening or closing the damper responsive to status of the damper request register and controlling status of the lockout register to indicate status of the damper, and the appliance control programmed processor may be configured for controlling status of the damper request register responsive to a call for operation of the gas burner and operating the gas burner only if the lockout register is in an unlock status.

A damper control device may include an appliance control programmed processor for controlling a gas burner, the appliance control programmed processor including a lockout register for storing electronic data information, and a damper control programmed processor for controlling a damper, the damper control programmed processor including a damper request register for storing electronic data information. The damper control programmed processor may be configured for selectively opening or closing the damper responsive to status of the damper request register and controlling status of the lockout register to indicate status of the damper, and the appliance control programmed processor may be configured for controlling status of the damper request register responsive to a call for operation of the gas burner and operating the gas burner only if the lockout register is in an unlock status.

A furnace including a combustion chamber for burning fuel can have increased fuel burning efficiency, increased heating efficiency, and decreased harmful emissions of combustion byproducts. A combustion air delivery system delivers primary and secondary combustion air to the combustion chamber. Primary and secondary combustion air may be delivered at amounts that increase burning efficiency. An amount of secondary combustion air can be controlled by a valve system. A heat transfer device efficiently transfers heat from products of combustion for heating an enclosed space.

A furnace including a combustion chamber for burning fuel can have increased fuel burning efficiency, increased heating efficiency, and decreased harmful emissions of combustion byproducts. A combustion air delivery system delivers primary and secondary combustion air to the combustion chamber. Primary and secondary combustion air may be delivered at amounts that increase burning efficiency. An amount of secondary combustion air can be controlled by a valve system. A heat transfer device efficiently transfers heat from products of combustion for heating an enclosed space.

A furnace inducer choke and a gas furnace employing the furnace inducer choke. In one embodiment, the furnace inducer choke includes: (1) a choke body configured to engage a furnace inducer blower, the choke body having an opening extending entirely therethrough to limit an amount of combustion air entering a furnace that the furnace inducer blower is attached, and (2) a tab protruding from the choke body a distance sufficient to identify the opening when the choke body and furnace inducer blower are installed in the furnace.

A furnace inducer choke and a gas furnace employing the furnace inducer choke. In one embodiment, the furnace inducer choke includes: (1) a choke body configured to engage a furnace inducer blower, the choke body having an opening extending entirely therethrough to limit an amount of combustion air entering a furnace that the furnace inducer blower is attached, and (2) a tab protruding from the choke body a distance sufficient to identify the opening when the choke body and furnace inducer blower are installed in the furnace.